Electroluminescent phosphorescent materials containing a heavy metal complex, such as Pt, Os and Ir complexes, have gained a lot of attention in the application as an emitter of an OLED due to their highly efficient luminescent property. Among these complexes the Ir complex is the most efficient. The Ir complex usually has a regular octahedron structure at a positive trivalent oxidation state, and its luminescent property mainly comes from a metal-to-ligand charge transfer triplet state-3MLCT or a ligand-based triplet state-3(π−π*) state. A highly efficient electroluminescent phosphorescent emission is caused by the electron configurations of these heavy metal complexes having a strong spin-orbit coupling.
U.S. Patent publication No. 2002/0034656A1 discloses an organometallic complex as an electroluminescent phosphorescent material including an octahedron complex, L2MX, where L and X are distinctive bidentate ligands, and M is Ir or Pt. Among the ligands (L) shown in FIG. 49 thereof, vinylpyridine is one of them. However, this published patent application does not propose the use of an Ir complex with vinylpyridine (L) as a ligand as an electroluminescent phosphorescent material. Furthermore, this published patent application does not actually synthesize the Ir complex having vinylpyridine as a ligand. The disclosure of this published U.S. patent application is incorporated herein by reference.